Conventional rotary drilling operations rotate the drill bit by turning the entire drill string at the surface with a rotary table and kelly. However, a down-hole motor, such as a down-hole mud motor, utilizes the circulation system and the hydraulic power of a drilling fluid to rotate the drill bit without rotating the entire drill string within the well bore. A down-hole mud motor system may include drill collars which are larger diameter pipes attached to the drill pipe at a lower end of the drill string above the drill bit wherein the drill collar helps to add weight to the drill string to ensure there is sufficient downward pressure to enable the drill bit to drill through the formation. The drill bit, located at the bottom end of the drill string is responsible for breaking up and dislodging the rock formation as small rock particles suspended in the fluid as it is pumped back to the surface from the drill bit. There are different types of drill bits, such as diamond bits, steel tooth bits, and carbide insert bits to handle different drilling conditions, such as the type of underground formation, the type of drilling, and the temperature of the Earth.
A mud motor is typically used in directional drilling operations, especially in oil and gas and mining operations. Mud motors are usually used to rotate a drill bit for bore hole drilling and coring in the earth. The rotor of the motor rotates the drill bit with respect to a stator which is connected to a drill string. The weight of the drill bit and drill string in conjunction with the rotary speeds generated by the mud motor enables the rotating drill bit to efficiently cut away the formation the drill bit is pushed against. Drilling fluid, such as so-called “mud”, supplies the hydraulic power to operate the motor. More particularly, the mud motor operates by converting the hydraulic energy of the drilling fluid into mechanical torque and applying the torque to drive the drill bit into the formation.
The additional main functions of the drilling fluid include cooling and lubricating the drill bit, stabilizing the wall of the well bore, controlling well pressure, and removing debris and cuttings. The composition of the mud drilling fluid used for any particular drilling operation depends on the drilling conditions. The mud must be of light enough consistency such that it may circulate through the drill bit to cool and lubricate the parts, but the mud must also be sufficiently viscous to carry the rock particulate debris away from the drill bit when the drill cuttings are circulated back up the well through the annular space. Typically, the circulating system pumps the mud drilling fluid down through the hollow drill string. The mud supplies the hydraulic power to operate the mud motor and cools and lubricates the drill bit as it flows through apertures in the drill bit. The mud may be a water-based, synthetic-based or diesel fuel-based product. Once the mud is circulated back up to the surface through the annular space, the cuttings are removed from the mud, for example, by way of a mesh before the mud is returned to the mud pits to be used again.
As the drilling fluid is pumped down the drill string and through the mud motor, pressure loss due to friction reduces the amount of pressure supplied to the motor, causing a decrease in motor torque and slower boring. Further pressure loss at the motor due to narrow flow passages also reduces the efficiency of drilling. By minimizing the pressure loss, the overall torque and hydraulic horsepower available to the motor may be increased. As such, there exists a need to provide a fluid driven drilling motor and system wherein pressure loss as the drilling fluid circulates through the drilling motor and system may be minimized to increase the drilling efficiency of the down-hole drilling motor.
Applicant is aware of several apparatus and methods in the art that purport to improve the efficiency of a down-hole motor. However, none of the prior art apparatus and methods minimize the pressure loss of the drilling fluid in the manner of the present invention. For example, applicant is aware of U.S. Pat. No. 6,561,290 to Blair et al. for a down-hole mud motor which has an improved bearing mandrel and a bearing stop to transfer a larger percentage of the weight of the drill string to the bit. Improved sealing systems for the transmission section and bearing section prevent drilling mud from entering critical components. A piston stop is provided to prevent the piston from damaging any parts as the piston moves under pressure. A compensating pressure disk is placed in the lower housing to prevent pressure from building up in the bearing section. A grooved ball seat is provided in the transmission to allow for greater flow of lubricant around the ball bearings.
Applicant is also aware of Canadian Patent No. 2,197,964 which issued to Sallwasser et al. on Dec. 3, 2002 for a Method and Apparatus for Drilling with a Flexible Shaft While Using Hydraulic Assistance. The apparatus and method disclosed includes applying thrust weight to a drill bit when drilling with a flexible drilling shaft while creating perforations in a cased well. The thrust is applied directly to the drill bit instead of applying it to the drill bit through the flexible drilling shaft. A support bracket is also in contact with a piston and is in slidable contact with the tool housing. A portion of the piston is positioned inside a chamber in the housing and is slidably attached to the chamber walls. As hydraulic fluid flows into the chamber opposite the piston, the piston is forced toward the drill bit. As the piston moves toward the drill bit, force is exerted on the support bracket which causes the bracket to move toward the drill bit. This force is transferred to the drill bit during the drilling process, thereby supplying the force needed by the drill bit to effectively drill through a desired material.
Applicant is also aware of U.S. Pat. No. 3,982,859 which issued to Tschirky et al. on Sep. 28, 1976 wherein the operation of hydraulic motors may be improved by employing stable flow restrictors which are resistant to corrosion and maintains a stable bypass volume of fluid used to lubricate the bearing package.